1. Technical Field
The present invention relates to an organic EL device applied to displays or display light sources, and more particularly, to a compound for organic EL desirably applied to a coat-type organic EL device and to an organic EL device using the same.
2. Related Art
Recently, the development of organic electro-luminescent devices (organic EL devices) using an organic electroluminescent element (organic EL element) which serves as a self-emission display for replacing a liquid crystal display has accelerated. With respect to such an organic EL device and a method of producing the organic EL device, JP-A-2000-323276 and JP-T-2002-536492 are examples of the related art.
A process were a host material and a light emitting dopant are used as a material of a light emitting layer is applied to a known organic EL device (organic EL apparatus) so as to assure high efficiency of light emission, a change in the color of emitted light, and a long life span. The process is frequently applied to organic EL devices including an organic material provided using deposition, but not to polymer-coat-type organic EL devices which include a layer formed using an inkjet process (liquid droplet jet process) or a spin coating process.
In connection with the meaning, the terms ‘host material and light emitting dopant’ have the following meanings. (1) The host material is capable of providing both holes and electrons.
The reasons (problem) why both the host material and the light emitting dopant are not frequently applied to the polymer-coat-type organic EL device are as follows.
(1) When a solution containing the host and the light emitting dopant is applied, bleeding of the light emitting dopant may occur. The reason is that, if the solution of materials having a low molecular weight is applied to the polymer and dried, the materials having a low molecular weight flow out from the surface layer during the drying.
(2) The light emitting dopant material has poor hole or electron trapping ability. When the host material is a conjugated polymer, the trapping ability is very poor. In such a conjugated polymer, it is believed that since the holes and the electrons preferentially flow through the host polymer molecule, it is difficult for the light emitting dopant to trap the holes and the electrons
(3) The development of the light emitting dopant material is time-consuming. The reason is that the system including the host and light emitting dopant is inefficient in the polymer-coat-type organic EL device field in comparison with the deposition type of EL (small-molecular-EL).